命令模式的使用

Question

I just started reading a book called "Game Programming Patterns". In the very beginning, a simple pattern called the command pattern was explained, and the example for it was to be able to configure the action that specific keys trigger. But, actually, I have a question on that. Why would you use Commands to trigger those actions instead of just doing something like:

Map<Key, Action> map
if(isPressed(key)) map.get(key).trigger()

The result would be the same, and frankly, it seems a bit more effective in my mind. Could anyone please explain to me why, in that situation, you would use the command pattern instead of my example above?

Command Pattern Example:

Command* this_specific_key_command;
if(isPressed(key)) this_specific_key_command.trigger()

Where the command class is something like

class Command{
    virtual void trigger() = 0;
}

Sorry for the messed up code. I hope it is understandable.

Answer 1

Actually your first implementation is exactly a command pattern. The definition of a command pattern is as follows:

The Command Pattern encapsulates a request as an object, thereby letting you
parameterize other objects with different requests, queue or log requests, and support
undoable operations.

The first sentence in this definition defines the command pattern. Both samples you provided are equivalent. In the first one you call the object Action, while in the second you call it Command. Both of these are exactly the same. They are the object (the definition refers to) that encapsulates the request.

It doesn't matter if you are storing a pointer or using a map to store these commands. The important thing is that these object have a method called trigger() that is encapsulating the request(or the action to be done).This is what makes the command pattern.